Wireless communication system for allocating transmission period

ABSTRACT

A system is provided for efficiently allocating a transmission period in a WLAN system. An access point (AP) transmits a PSMP message providing a downlink period and an uplink period provided to each station (STA), and at least one sub PSMP frame indicating a period of at least one of a downlink and an uplink for an STA requiring additional resource allocation. After exchanging data with the AP in the downlink and uplink periods provided by the PSMP frame, if there is a need for additional resource allocation, the STA receives the at least one sub PSMP frame and exchanges data with the AP in the period provided by the each sub PSMP frame.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of anapplication entitled “Phase Resource Allocation Method” filed in theUnited States Patent and Trademark Office on Oct. 18, 2005 and assignedSer. No. 60/727,915, an application entitled “Multi-Phase ResourceAllocation Method” filed in the United States Patent and TrademarkOffice on Oct. 27, 2005 and assigned Ser. No. 60/730,924, andapplication entitled “Method and Apparatus for Allocating TransmissionPeriod in a Wireless Communication System, and System Therefor” filed inthe Korea Intellectual Property Office on Jun. 8, 2006 and assignedSerial No. 2006-51604, the entire contents of all of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a wireless communicationsystem, and in particular, to a system for efficiently allocating atransmission period in a transmission frame period of a wireless networksystem.

2. Description of the Related Art

Along with the recent development of wireless communication technologiesand the resulting spread of wireless equipment, there is an increasingdemand for high-speed, highly-reliable data transmission via a wirelesslink. A Wireless Local Area Network (WLAN) developed to meet the demandis basically composed of stations (STAs), which are mobile datacommunication equipment, and an access point (AP) capable of exchangingdata with the STAs. The AP and the STAs, located in the same wirelessservice coverage area, are known as a Base Service Set (BSS).

In a WLAN system, STAs located in one wireless service coverage areatransmit or receive data using wireless resources allocated from an AP.In this case, the AP allocates the wireless resources in the form ofphase resources, and the term “phase resources” refers to a period inwhich the STAs or AP can transmit data.

FIG. 1 illustrates a structure of a transmission frame period in aconventional WLAN system.

Referring to FIG. 1, in a transmission frame period 100 having a fixedlength determined in the system, an AP transmits a MAP (mapping) frame110 indicating phase resource allocation for the full transmission frameperiod 100. The MAP frame 110 is composed of a downlink MAP 120indicating a period in which the AP can transmit data, and an uplink MAP122 indicating a period in which the STAs can transmit data. Thedownlink MAP 120 is composed of a Number-of-STAs field 130, and at leastone STA Information field 132 determined based on the Number-of-STAsfield 130. Similarly, the uplink MAP 122 is composed of a Number-of-STAsfield 134, and at least one STA Information field 136 determineddepending on the Number-of-STAs field 134. The STA Information fields132 and 136 each include STA ID fields 140 and 144 indicating downlinkor uplink periods allocated to the STAs, and Time Offset fields 142 and146 indicating time offsets allocated to the STAs.

An STA, that has been allocated a period in the MAP frame 110, receivesdata in a period indicated by corresponding STA information, of adownlink period 112, and transmits data in a period indicated bycorresponding STA information, of an uplink period 114. The STA holds asleep mode in the other period except for the period in which the MAPframe 110 is transmitted and the period indicated by the MAP frame 110.A contention period 116 following the uplink period 114 can be accessedby at least one STA on a contention basis.

In this way, the AP estimates the amount of resources required for eachSTA in one transmission frame period 100, and allocates downlink anduplink periods according to the estimation. However, when the APoverestimates the amount of resources required for the STA, the wirelessresources are wasted, decreasing data throughput performance. In thiscase, the STA may not use the allocated wireless resources. Moreoverthat resource can not be reused by other STAs since that resource isalready allocated to the particular STA. When the AP underestimates theamount of resources required for the STA, the STA cannot be allocatedits required resources until at least the next transmission frameperiod, suffering transmission delay and jitter of the uplink service.The transmission delay and jitter affects a Quality of Service (QoS)required by the STA. In addition, if the STA accesses the contentionperiod 116 due to a lack of its allocated resources, the STA cannotoperate in the sleep mode for the contention period, wasting its power.

Therefore, in the wireless communication system in which the APdetermines the downlink and uplink periods required for the STA throughscheduling, there is a need for technology for preventing the reductionin data throughput and the waste of STA power, and efficientlyallocating downlink and uplink periods.

SUMMARY OF THE INVENTION

To substantially solve at least the above problems and/or disadvantagesand to provide at least the advantages below, the present inventionprovides a transmission period allocation system for minimizing a wasteof STA power without reducing data throughput in a wirelesscommunication system.

The present invention provides a system for flexibly allocating atransmission period required for an STA using more than two MAP framesin a wireless communication system.

According to one aspect of the present invention, there is provided awireless network system including an access point (AP) for transmittinga PSMP frame providing a downlink period and an uplink period allocatedto at least one station (STA), and at least one sub-PSMP frame providingat least one of an additional downlink period and an additional uplinkperiod to at least one STA requiring additional resource allocation, theadditional downlink period being provided in the frame period if thereis additional data to be received by the STA and the additional uplinkperiod being provided in the frame period if there is additional data tobe transmitted by the STA; and an STA for receiving from the AP the PSMPframe and the sub-PSMP frame, receiving data from the AP in the downlinkperiod provided by the PSMP frame and transmitting data to the AP in theuplink period provided by the PSMP frame, and receiving data in theadditional downlink period provided by the sub-PSMP frame if there isadditional data to be received, and transmitting data in the additionaluplink period provided by the sub-PSMP frame if there is additional datato be transmitted.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a diagram illustrating a structure of a transmission frameperiod in a conventional WLAN system;

FIG. 2A is a diagram illustrating a configuration of a WLAN systemaccording to the present invention;

FIG. 2B is a block diagram illustrating an exemplary structure of an APand each STA in the WLAN system shown in FIG. 2A;

FIG. 3 is a diagram illustrating a structure of a transmission frameperiod according to the present invention; and

FIG. 4 is a timing diagram illustrating a power reduction effect of thephase resource allocation according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the annexed drawings. In the followingdescription, a detailed description of known functions andconfigurations incorporated herein has been omitted for clarity andconciseness.

A main feature of the present invention, which is related to allocationof transmission periods in a wireless communication system, is toprovide more than one MAP (mapping) frames to indicate a periodallocated by an access point (AP) to each station (STA) in atransmission frame period.

The allocated period starts immediately after the MAP frame istransmitted, and in the transmission frame period, the MAP frames otherthan the first MAP frame will be referred to as “subsequent MAPs (subMAPs).”

Although a detailed description of the present invention will be madewith reference to a Wireless Local Area Network (WLAN) system based onIEEE 802.11 standards, it will be understood by those skilled in the artthat allocation of phase resources, a basic object of the presentinvention, can also be applied to other wireless communication systemshaving similar technical requirements and channel formats withoutdeparting from the spirit and scope of the invention.

FIG. 2A illustrates a configuration of a WLAN system according to thepresent invention.

Referring to FIG. 2A, each of APs 202 and 210 is connected to a wirenetwork 200, and a plurality of STAs 204, 206, 208, 212 and 214 accesstheir associated APs 202 and 210 via an IEEE 802.11 Physical (PHY) layerand a wireless link based on a Media Access Control (MAC) protocol, andtransmit/receive data over a plurality of wireless channels. The STAs204 to 208 and the AP 202, located in the same wireless service coveragearea 220, constitute one Base Service Set (BSS). In the same way, theSTAs 212 and 214 and the AP 210, located in the wireless servicecoverage area 222, form another BSS. STAs located in each BSS canexchange data with each other via a corresponding AP. The key functionsof the APs 202 and 210 include delivery of data traffic, access toanother network (e.g. wire network 200), roaming support,synchronization in a BSS, power management support, and control of mediaaccess for supporting time-bound service in a BSS.

FIG. 2B is a block diagram illustrating an exemplary structure of an APand each STA in the WLAN system shown in FIG. 2A. Both of the AP and theSTA can include a display 232, a processor 234, a transceiver 236, aninput unit 238, a storage 240, a Random Access Memory (RAM) 242, a ReadOnly Memory (ROM) 244, and a common bus 230. The illustrated exemplarystructure is merely provided for convenience. Although specific elementsand their operations of a computer system serving as an AP or an STAwill be described herein with reference to FIG. 2B, the exemplarydescription should not limit the present invention.

Referring to FIG. 2B, the transceiver 236, connected to an antenna (notshown), receives desired data and converts the received signal intocorresponding digital data. The processor 234 is a controller operatingunder the control of an operating system (OS) and other programs,included in the ROM 244, and the data and information generated by anoperation of the processor 234 are stored in the RAM 242.

The key operations of the processor 234 included in the AP includegeneration/analysis of data, allocation of periods for the STAs locatedin the same wireless service coverage area and connected to the AP,generation of at least one MAP frame indicating the allocated period,and operation mode control for the transceiver 236 based on theallocated period. Specifically, the processor 234 of the AP allocatesinitial resources R_(init) to the STAs through a MAP frame located inthe first part of a transmission frame, and if there is a need foradditional resource allocation, the processor 234 additionallyallocates, for uplink/downlink transmission, the remaining period in thetransmission frame period to at least one STA requiring the additionalresource allocation, through the sub MAP frame transmitted immediatelyafter a sequence duration associated with the first MAP frame of thetransmission frame. It would be obvious to those skilled in the art thatthe term “immediately after” substantially refers to a lapse of apredetermined time.

After the expiration of the downlink/uplink period indicated by thefirst MAP frame, if necessary, more than one sub MAP frames indicatingthe downlink and/or uplink periods allocated in the same transmissionframe period can be additionally transmitted. The sub MAP frame isfollowed by the downlink and/or uplink periods indicated by the sub MAPframe.

The key operations of the processor 234 included in the STA includegeneration/analysis of data, generation of a transmission frame, andoperation mode control for the transceiver 236 based on a MAP framereceived from the start point of the transmission frame. That is, theprocessor 234 controls the transceiver 236 such that it receives the MAPframe from the AP at the start point of every transmission frame, andanalyzes the MAP frame to determine whether its own STA ID(identification) is included therein. If its own STA ID is included inthe MAP frame, the processor 234 stores in the storage 240 informationrelated to the allocated downlink and uplink periods indicated by theSTA information associated with the STA ID, and then wakes up both areceiver and a transmitter of the transceiver 236 in the downlink anduplink periods so as to receive/transmit the data. The receiver and thetransmitter of the transceiver 236 enter the sleep mode in the otherperiods except for the allocated periods. Further, the processor 234 ofthe STA monitors whether a sub MAP frame indicating additionallyallocated resources is received from the AP after the expiration of thefull period indicated by the MAP frame, and upon receipt of the sub MAPframe, analyzes the received sub MAP frame.

FIG. 3 illustrates a structure of a transmission frame period accordingto the present invention. Although it is illustrated herein that framesand uplink/downlink periods are adjacent, intervals fortransmission/reception switching and processing may exist in the actualsystem.

Referring to FIG. 3, in a transmission frame period 300 having a fixedlength, an AP first transmits a MAP frame 310 a with a basic rate set(including modulation scheme, coding rate, and data rate), which is lessthan a normal rate set. This is to enable all STAs in the servicecoverage area to receive the MAP frame 310 a. Initially, the MAP frame310 a is periodically transmitted according to a fixed period (forexample, about 20 ms and 100 ms for Voice over Internet Protocol (VoIP)and Moving Picture Experts Group 4 (MPEG4), respectively) determinedthrough a negotiation between the AP and the STA. The transmission frameperiod 300 is initialized by the transmission of the MAP frame 310 a.

For example, the MAP frame 310 a, in order to indicate phase resourceallocation of its succeeding downlink period 312 and first uplink period314 a, is composed of a downlink MAP 320 indicating a period in whichthe AP can transmit data in the downlink period 312, and a first uplinkMAP 322 a indicating a period in which the STA can transmit data in thefirst uplink period 314 a. The downlink MAP 320 is composed of aNumber-of-STAs field 330 and at least one STA Information field 332determined based on the Number-of-STAs field 330. In the same way, thefirst uplink MAP 322 a is composed of a Number-of-STAs field 334 a andat least one STA Information field 336 a determined based on theNumber-of-STAs field 334 a.

The STA Information fields 332 and 336 a each include STA ID fields 340and 344 a that indicate STAs that have been allocated the periods in thedownlink period 312 and the first uplink period 314 a, Time Offsetfields 342 and 346 a that indicate start times of the periods allocatedto the STAs, and Duration fields 343 and 348 a that indicate the lengthsof the allocated periods. The STA ID fields 340 and 344 a each includeat least a part of an Association Identity (AID) of each STA, or atleast a part of a hardware address, i.e. a MAC address, given to eachSTA. An STA ID that indicates a period for broadcast/multicast data isset to a particular value, for example, ‘0’. The Time Offset fields 342and 346 a each indicate an interval from the MAP frame 310 a to a starttime of a corresponding period as a multiple of a predetermined unit oftime (for example, 4 μs). The Duration fields 343 and 348 a eachindicate an interval from a start time to an end time of the period,i.e. indicate a length of the period, as a multiple of a predeterminedunit of time (for example, 16 μs).

The first uplink MAP 322 a of the MAP frame 310 a indicates an uplinkperiod first allocated for the STA, and can be determined according to arequired data rate for individual service joined by each STA, or theamount of data estimated by the AP. The STA, allocated a period by theMAP frame 310 a, receives data in the period indicated by thecorresponding STA information 332, in the downlink period 312, andtransmits data in the period indicated by the corresponding STAinformation 336 a, in the first uplink period 314 a. The downlink anduplink data can include MPDUs including one or more Aggregate MACProtocol Data Unit (PDU) (A-MPDU) and/or payload, and anAcknowledgement. The STA maintains the sleep mode in the period wherethe MAP frame 310 a is transmitted, and the other periods except for theperiods indicated by the MAP frame 310 a.

After transmitting the data in the allocated period of the first uplinkperiod 314 a, each STA determines whether there is a need for additionalresource allocation. The need for additional resource allocation isdetermined based on whether there is additional transmission data, orwhether there is information to receive from the AP. A detaileddescription thereof will be omitted in order not to obscure the clearunderstanding of the present invention. An STA requiring additionalresource allocation, monitors a sub MAP frame 310 b after expiration ofthe first uplink period 314 a. The sub MAP frame 310 b can indicate thedownlink and/or uplink resources additionally allocated by the AP, andit is shown in FIG. 3 that the sub MAP frame 310 b indicates allocationof additional uplink resources, by way of example.

That is, the sub MAP frame 310 b includes a second uplink MAP 322 bindicating phase resource allocation for its succeeding second uplinkperiod 314 b. Similarly, the sub MAP frame 310 b can be transmitted withthe basic rate set. The second uplink MAP 322 b is composed of aNumber-of-STAs field 334 b and at least one STA Information field 336 bdetermined based on the Number-of-STAs field 334 b. The STA Informationfield 336 b includes an STA ID field 344 b that indicates an STAallocated a period in the second uplink period 314 b, a Time Offsetfield 346 b that indicates a start time of the period allocated to theSTA, and a Duration field 348 b that indicates a length of the period.The elements of the STA Information field 336 b have been describedabove. An STA, allocated phase resources by the sub MAP frame 310 b,receives data in the period indicated by the corresponding STAinformation 336 b, of the second uplink period 314 b.

Although not illustrated, if there is another need for additionalresource allocation, more than one sub MAP frames and an uplink periodor a downlink period based on the sub MAP frames can be additionallyincluded in the transmission frame period 300. A transmission schemeusing a MAP frame capable of accompanying one or more sub frames isreferred to as a Multi-Phase “Power Save Multi-Poll (PSMP),” and the MAPframe 310 a and the sub MAP frame 310 b are referred to as a PSMP frameand a sub PSMP frame, respectively. Each of the PSMP frame and the subPSMP frame is followed by at least one downlink or uplink periodindicated by the corresponding (sub) PSMP frame, and one (sub) PSMPframe and a corresponding period are referred to as a (sub) PSMPsequence. In other words, one PSMP sequence is initialized bytransmitting the PSMP frame, and the STA wakes up only in the periodindicated by the PSMP frame in the PSMP sequence starting with the PSMPframe, thereby minimizing power consumption.

A contention period 316 following the last sequence duration can beaccessed by at least one STA on a contention basis.

It should be noted that elements of the MAP frames 310 a and 310 b shownin FIG. 3 and their arrangements are subject to change without departingfrom the spirit and scope of the invention. For example, each of the MAPframes 310 a and 310 b includes one STA ID field, Time Offset andDuration fields for downlink transmission, and Time Offset and Durationfields for uplink transmission. In this case, if no period is allocatedto the uplink or downlink, a corresponding Duration field is set to Null(0). In addition, each of the MAP frames 310 a and 310 b can include afield for indicating whether it will be followed by another sub MAPframe. The STA analyzes the field in the sub MAP frame to determinewhether the sub MAP frame is the last sub MAP frame in the currenttransmission frame period.

FIG. 4 is a timing diagram illustrating a power reduction effect of thephase resource allocation according to the present invention.

Referring to diagram (a) of FIG. 4, a transmission frame period 400includes a MAP frame 410 a, a downlink period 412, a first uplink period414 a, a sub MAP frame 410 b, and a second uplink period. The MAP frame410 a indicates phase resource allocation of the downlink period 412 andthe first uplink period 414 a.

Diagram (b) of FIG. 4 shows a scenario in which the resources of thefirst uplink period 414 a allocated by the MAP frame 410 a are enough totransmit data and control messages desired by the STA. That is, afterswitching to the sleep mode after receipt of the MAP frame 410 a in aperiod 420, the STA wakes up in an allocated period 422 in the downlinkperiod 412 indicated by the MAP frame 410 a and receives data from theAP. After switching back to the sleep mode upon expiration of the period422, the STA maintains the sleep mode until an allocated period 424 inthe first uplink period 414 a indicated by the MAP frame 410 a. In theperiod 424, the STA transmits data and/or control messages to the AP.Here, the STA, as it has no need for additional resource allocation,holds the sleep mode until it receives a MAP frame of the nexttransmission frame period, without monitoring receipt of the sub MAPframe 410 b.

Diagram (c) of FIG. 4 shows a scenario in which after expiration of thefirst uplink period 414 a allocated by the MAP frame 410 a, there is aneed for additional resource allocation for the STA. That is, afterswitching to the sleep mode after receipt of the MAP frame 410 a in aperiod 430, the STA wakes up in an allocated period 432 in the downlinkperiod 412 indicated by the MAP frame 410 a, and receives data from theAP. After switching back to the sleep mode upon expiration of the period432, the STA maintains the sleep mode until an allocated period 434 inthe first uplink period 414 a indicated by the MAP frame 410 a. In theperiod 434, the STA transmits data to the AP. Here, the STA, as itrequires additional resource allocation, wakes up again in a period 436and monitors receipt of the sub MAP frame 410 b. Upon receipt of the subMAP frame 410, the STA switches back to the sleep mode and waits untilperiod 438 in a second uplink period 414 b indicated by the sub MAPframe 410 b. In the period 438, the STA transmits data to the AP.Although not illustrated, there is a possible allocated period mapped toadditional one or more MAP frames before expiration of the transmissionframe period 400.

As can be understood from the foregoing description, even though theamount of resources estimated by the AP is not accurate, the presentinvention minimizes a waste of resources and a reduction in the datathroughput, and maximizes the time in which the STA maintains the sleepmode without unnecessarily monitoring the downlink or uplink, reducingpower consumption of the STA. In addition, the present invention canperform additional resource allocation required for the STA in thecurrent frame period, without reserving the additional resourceallocation until the next transmission frame period.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A wireless network system, comprising: an access point (AP) totransmit a power save multi-poll (PSMP) frame allocating a downlinkperiod and an uplink period in a frame period, and to transmit asubsequent PSMP frame allocating at least one of an additional downlinkperiod and an additional uplink period in the frame period to provide anadditional resource allocation; and a station (STA) to receive from theAP the PSMP frame and the subsequent PSMP frame, to receive data fromthe AP during the downlink period and transmit data to the AP during theuplink period, and to receive data from the AP during the additionaldownlink period in response to there being additional data to bereceived and transmit data to the AP during the additional uplink periodin response to there being additional data to be transmitted.
 2. Thewireless network system of claim 1, wherein the PSMP frame comprises: anidentifier (ID) of the STA; a start offset indicating a start point ofthe downlink and uplink periods provided by the PSMP frame; and aduration field indicating a length of the downlink and uplink periodsprovided by the PSMP frame.
 3. The wireless network system of claim 1,wherein the uplink period provided by the PSMP frame is allocatedaccording to a required data rate.
 4. The wireless network system ofclaim 1, wherein the subsequent PSMP frame comprises: an identifier (ID)of the STA; a start offset indicating a start point of each periodprovided by the subsequent PSMP frame; and a duration field indicating alength of each period provided by the subsequent PSMP frame.
 5. Thewireless network system of claim 1, wherein the downlink and uplinkperiods provided by the PSMP frame and the at least one of theadditional downlink period and the additional uplink period provided bythe subsequent PSMP frame are included in one transmission frame periodhaving a fixed length.
 6. A wireless network system, comprising: anaccess point (AP) to transmit a power save multi-poll (PSMP) frameallocating a downlink period and an uplink period in a frame period, andto transmit a subsequent PSMP frame allocating at least one of anadditional downlink period and an additional uplink period in the frameperiod to provide an additional resource allocation, wherein thesubsequent PSMP frame is an additional PSMP frame to follow the PSMPframe in the frame period having a periodic duration; and a station(STA) to receive from the AP the PSMP frame and the subsequent PSMPframe, to receive data from the AP during the downlink period andtransmit data to the AP during the uplink period, and to receive datafrom the AP during the additional downlink period in response to therebeing additional data to be received and transmit data to the AP duringthe additional uplink period in response to there being additional datato be transmitted.